1. Field of the Invention
The present invention relates in general to power steering systems for automotive vehicles and more particularly to a power steering system of the type having a fail-safe mechanism.
2. Disclosure Information
A power steering system of the type having such a fail-safe mechanism is disclosed in Japanese Utility Model Provisional Publication No. 62-118782 for instance. This power steering system includes a means for detecting a steering torque or effort applied to a steering gear by way of a steering wheel, a steering assist force transmitting means connected to the steering gear for supplying thereto a steering assist force, and a control means for controlling increase and decrease of a steering assist force to be produced by an electric motor in accordance with an output signal from the steering effort detecting means, whereby when the average of the detected steering efforts becomes larger than a predetermined value under a straight-ahead vehicle running condition, the system determines that a malfunction has occurred and gives warning to the driver. After issuance of the warning, the fail-safe mechanism is put into action for reducing the steering assist force (assist gain) produced by the electric motor.
With the prior art power steering system, the warning to the driver is given by means of a warning lamp or by a device for producing a warning sound. However, there is a possibility that such warning is overlooked by the driver when, for example, his attention is being attracted to the outside of the vehicle or he is listening to the stereo. In such a case, the driver shall feel from the next time of steering operation and onward that the turning operation of the steering wheel has unexpectedly changed to require a more effort, i.e., the operation feel of the steering wheel has unexpectedly changed heavier and therefore the operation feel has become worse, inevitably leading to deterioration of its image or reputation as a merchandise.